In truth, the Republican base is no larger than 25%, probably less. Much of that support is garnered by hoodwinking deeply religious Southerners voting against their economic interests. Gerrymandering, a significant fraction who simply don't bother, and the sizeable US "independent" vote which swings both ways (double entendre intended) is the only reason they are a significant party with election wins. What support they do have, however, is very powerful - especially the Right Wing media. Mobilizing that independent vote and the Southern Strategy has been their strenght over the last 40 years. They couldn't win a one-horse race for most of the 20th century.
25% is probably near the correct level (maybe a smidge high) without the science of marketing making their products "saleable". There may be some blowback from the Giffords shooting, but the figure seems sensible.
Although there is far wider support for the Democratic Party, the real story is the great apathy of the American voter at large. If the Dems decided to actually distinguish themselves from Republican candidates on economic issues, they (Repubs) would not win another election in this country. However, since the Dems have far wider popular support, AND since they are more effective managers of the neoliberal enterprise, Sarah Palin is being supported by powerful interests in order to drive a stake into the Republican Party.
Does anyone disagree?